05 Jul 2024
 | 05 Jul 2024
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

Lagrangian characterization of heat waves: The perspective matters

Amelie Mayer and Volkmar Wirth

Abstract. Although heat waves are one of the most dangerous types of weather-related hazards, their underlying mechanisms are not yet sufficiently understood. Especially, there is still no scientific consensus about the relative importance of the three key processes: horizontal temperature transport, subsidence accompanied by adiabatic heating, and diabatic heating. The current study quantifies these processes using a Eulerian method based on tracer advection, which allows one to extract Lagrangian information. For each grid point at any time, the method yields a decomposition of temperature anomalies into the aforementioned processes, complemented by the contribution of a pre-existing anomaly. Two different approaches for this decomposition are employed. The first approach is based on full (absolute) fields of the respective terms, whereas the second approach is based on anomaly fields of the respective terms, i.e., deviations from their corresponding climatologies. The two approaches offer two distinct perspectives on the same subject matter. By analyzing two recent heat waves, it is shown that the two decompositions yield substantial differences regarding the relative importance of the processes. A statistical analysis indicates that these differences are not coincidental, but characteristic for the respective regions. It is concluded that the Lagrangian characterization of heat waves is a matter of perspective.

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Amelie Mayer and Volkmar Wirth

Status: open (until 29 Aug 2024)

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Amelie Mayer and Volkmar Wirth
Amelie Mayer and Volkmar Wirth


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Short summary
Although heatwaves are among the most dangerous weather-related hazards, their underlying mechanisms are not fully understood. Here, we investigate the formation of heat waves in an air-parcel based framework and distinguish the contributions from horizontal transport, vertical transport, and diabatic heating. We show that the obtained results depend profoundly on whether one compares the absolute contributions of the individual terms or, instead, their anomalies relative to climatology.